In the rapidly expanding field of vacuum transport techniques, in particular in connection with water-miser vacuum closets and drain pipes, non-return valves are of great importance and, in some cases, have come to serve new purposes.
Prior art non-return valves for pressure systems in most cases are far too heavy and unwieldy and, needless to say, too robust in systems where the pressure difference rarely exceeds 0.05 MPa. Novel constructions exist where regard has been paid to the above deficiencies in that the valves have been made of plastic and provided with connecting sockets instead of flanges but where, nonetheless, the particular drawbacks have remained.
A special problem in vacuum-operated closet devices used in mobile units, such as boats and railway carriages, is that the non-return valve must be located at the highest point of the system. In actual practice, this means in most cases that the valve must be disposed immediately under a ceiling. In extant constructions, the service or inspection cover on the non-return valve will then be located at a distance of only a few centimeters from the ceiling and, hence, it will be difficult to remove the screws securing the inspection cover. When, despite such difficulties, the cover has been removed and it has been established that the valve is leaking because the flap is worn out and there is no spare flap at hand, a long stoppage of the system may be necessary.
Also, the valves hitherto used must be mounted for through-flow in the right direction, since, if the valves are incorrectly mounted, which occurs more often than may be imagined even with experienced fitters, the system will not work and so the valve must be dismounted and reversed, which not only entails increased costs but also is a source of irritation.